Absolute position sensor using Hall array

ABSTRACT

A system for determining an absolute position of a device includes a high resolution track ( 14 ), a sensor and processing unit ( 22 ) associated with the high resolution track ( 14 ), a reference track ( 18 ) having a plurality of pole pairs arranged to define a single-track Gray code segment, and an array of Hall effect sensors ( 26 ) associated with the reference track to output a reference signal to the sensor and processing unit indicative of the coarse absolute position of the device over the single-track Gray code segment. The sensor and processing unit ( 22 ) combines the reference signal with the position of the device over the high resolution track to determine an initial, fine absolute position of the device. An up/down hardware counter ( 34 ) increments the initial fine absolute position using a signal generated from the high resolution track, and without any further software-based processing, to maintain and continuously update the fine absolute position of the device.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/438,704 filed on Dec. 23, 2016, the entire content ofwhich is hereby incorporated herein by reference.

BACKGROUND

The present invention relates to position sensing systems and methods.

Various absolute position sensors and associated signal processingtechniques are known for determining an absolute position of a rotatingor linearly-moving target. For example, U.S. Pat. No. 8,058,868discloses one such example of an off axis magnetic sensor that uses atwo-track, multi-pole magnetic target with evenly-spaced and sized highresolution magnetic poles. The entire specification of U.S. Pat. No.8,058,868 is hereby incorporated by reference herein. The '868 patentdescribes how to use a high resolution Hall effect sensor like theTimken MPS160 or MPS512 sensor chip to detect local absolute positionover a magnetic pole pair. The '868 patent shows how to use a secondtrack with one or more pole pairs to generate a coarse or low resolutionabsolute position signal that can then be used together with a highresolution Hall effect sensor like the Timken MPS160 or MPS512 sensorchip to determine a fine or high resolution absolute position over alonger arc or longer linear range.

Also known is the use of Gray code encoding on magnetic encoders. Graycode encoding is a system of binary counting in which any two adjacentcodes differ by only one bit position. It is possible to arrange severalsensors adjacent a single track (ring or linear) so that consecutivepositions differ at only a single sensor. The result is the single-trackGray code encoder. This concept can be used for the reference track ofthe encoder described in the '868 patent such that the signal from thereference-track Gray code can be combined with the signal from the highresolution Hall effect sensor, processed using software on theprocessor, and then outputted as a fine or high resolution absoluteposition signal.

SUMMARY

The present invention contemplates improvements to the sensorarrangements and signal processing described above. In one embodiment,the latency or processing time conventionally required to repeatedly orcontinuously calculate the fine or high resolution absolute positionwith conventional software and processors can be greatly reduced.Conventionally, the processing chip, which can be internal or externalto the high resolution sensor or incorporated into the high resolutionsensor, must repeatedly combine and process the output signal from thereference track with the output signal from the high resolution track todetermine the fine absolute position. According to one embodiment of thepresent invention, after the initial fine absolute position calculationis completed one time by the processing chip, the system then uses anup/down count signal to continuously, or on demand, update the fullabsolute position reading without any further software processing. Theabsolute position is maintained in an up/down hardware counter. Such ahardware counter can increment or decrement independently of anysoftware. This results in a fine or high resolution absolute positionoutput signal that is achieved more quickly and efficiently thanconventional software-generated signals, as it is delayed only by thelogic timing associated with the up/down counter for each change inposition, and not by any processing times associated with the softwareor processor.

In another embodiment, the resolution of encoders utilizing asingle-track Gray code arrangement can be improved via modification. Athird track is added to further subdivide the number of positions thatcan be determined by the single-track Gray code arrangement of thereference track. When combined with the signal from the high-resolutiontrack and the reference track, the encoder can achieve an increasedresolution.

In another embodiment, the resolution of encoders utilizing asingle-track Gray code arrangement can be improved via a differentmodification. The inventive reference track is configured with amodified single-track Gray code that defines 2 or more distinct segmentsof the reference track (ring or linear), each segment having its ownGray code (which can all be the same Gray code or different Gray codes).A third track is then added and can be used to identify each distinctGray code segment to construct higher resolution absolute positiondetection over one revolution or length of the encoder. The use ofmultiple Gray code segments on the reference track also enables areduction in the physical space needed for the Hall array associatedwith the reference track, and can also help to reduce the overall systemcost.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 show a first absolute position sensing system embodying theinvention.

FIG. 5 illustrates alternative signal-types that can be used.

FIG. 6 illustrates a method of verifying the absolute position signalgenerated by the first absolute position sensing system of FIGS. 1-4.

FIG. 7 shows a second absolute position sensing system embodying theinvention.

FIG. 8 shows a third absolute position sensing system embodying theinvention.

FIG. 9 shows a fourth absolute position sensing system embodying theinvention.

FIG. 10 illustrates an alternative signal processing flow to FIG. 4.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

As should also be apparent to one of ordinary skill in the art, thesystems shown in the figures are models of what actual systems might belike. As noted, many of the modules and logical structures described arecapable of being implemented in software executed by a microprocessor ora similar device or of being implemented in hardware using a variety ofcomponents including, for example, application specific integratedcircuits (“ASICs”). Terms like “processing unit” may include or refer toboth hardware and/or software. Furthermore, throughout the specificationcapitalized terms are used. Such terms are used to conform to commonpractices and to help correlate the description with the coding examplesand drawings. However, no specific meaning is implied or should beinferred simply due to the use of capitalization. Thus, the claimsshould not be limited to the specific examples or terminology or to anyspecific hardware or software implementation or combination of softwareor hardware.

FIGS. 1-4 illustrate a first absolute position sensing system 10. Withreference to FIG. 1, the first sensing system 10 includes a firstmulti-polar magnetic ring or high resolution track 14, which includestwenty-five magnetic pole pairs or North/South pole pairs. Each pole ofeach North/South pole pair is the same size (e.g., arc length). A secondmulti-polar magnetic ring or a reference track 18 is positionedconcentrically within the high resolution track 14. In the embodimentshown, the reference track 18 includes four magnetic pole pairs orNorth/South pole pairs. The illustrated pole pairs of the referencetrack 18 are arranged to define what is known as a single-track Graycode. Gray encoding is a system of binary counting in which any twoadjacent codes differ by only one bit position. It is possible toarrange several sensors adjacent to a single track (ring or linear) sothat consecutive positions differ at only a single sensor, therebyallowing the sensor array to determine an absolute position about thesingle-track Gray code segment. As shown in FIG. 1, the single-trackGray code configuration is a single segment that extends over the entirearc length of the circular reference track 18. FIG. 3 illustrates theGray code segment of the reference track 18 stretched linearly, andillustrates how an array of 6 Hall effect sensors can determine a coarseposition among 48 possible positions along the single-track Gray codesegment. As will be explained below, other embodiments can include areference track having two or more single-track Gray code segments thattogether extend over the 360 degree arc length of the reference track.

It should be noted that the high resolution track 14 can have more orfewer magnetic pole pairs in other embodiments. Similarly, the referencetrack 18 can have more or fewer magnetic pole pairs in otherembodiments. Additionally, the orientation of the reference track 18being within the high resolution track 14 could be reversed, such thatthe reference track 18 is outside the high resolution track 14.Furthermore, while shown as circular tracks, those skilled in the artwill understand that parallel linear tracks could be used instead ofconcentric or radial circular tracks.

FIG. 2 illustrates the sensors associated with the high resolution track14 and the reference track 18 of FIG. 1. The tracks 14, 18 are shownschematically in FIG. 2 without the pole pairs illustrated. A sensor andprocessing unit 22 is associated with the high resolution track 14 andis configured to determine a position of the device over one of theNorth/South pole pairs of the high resolution track 14. The processingunit 22 takes the form of a sensing ASIC, such as a Timken MPS160 orMPS512 chip, and is capable of determining the absolute position of atarget magnet within one North/South pole pair of the high resolutiontrack 14 only. The processing unit 22 can also generate a referencepulse signal that indicates a center position of the one North/Southpole pair. The processing unit 22 includes an internal sensor array 24(see FIGS. 7-9) to generate an output that is indicative of an angularposition of a pole pair under the processing unit 22. It should beappreciated that the internal sensor array 24 can include a string ofsensing elements such as Hall effect sensors. It should be understoodthat the processing unit 22 can include an optional interface forinterfacing with components external to the processing unit 22.

An array of Hall effect sensors 26 is associated with the referencetrack 18 and is configured to determine a coarse absolute position ofthe device over the single-track Gray code segment and to output areference signal to the processing unit 22 indicative of the coarseabsolute position of the device over the single-track Gray code segmentof the reference track 18. While six Hall effect sensors are shown inthe array 26, other embodiments can use different numbers of sensors.The distance between adjacent sensors 26 can be equal, but can be longerthan a pole length of one or more poles on the reference track 18. Withthe coarse absolute position determined by the reference track 18, theprocessing unit 22 combines the reference signal with the position ofthe device over one of the North/South pole pairs of the high resolutiontrack 14 to determine an initial, fine absolute position of the device.For a rotary encoder, this can be an absolute mechanical angle/angularposition of a target/target wheel.

After the initial fine absolute position calculation is completed onetime by the sensor and processing unit 22, the system 10 then uses anup/down count signal to continuously, or on demand, update the fineabsolute position reading without any further software processing. FIG.4 schematically illustrates this usage of an up/down data counter. Asshown in FIG. 4, the initial fine absolute position of the device isrepresented in box 30. In some embodiments, the initial absolute valuerepresented in box 30 could be the summation of the detected initialabsolute value plus an offset value specific to a customer application.In this manner, the start position (e.g., 0 position) of the absoluteencoder can be set for a specific customer application. This offsetcapability can alternatively be achieved in the manner discussed belowwith respect to FIG. 10. This initial absolute value 30 is loaded intoan up/down counter 34 (which can be a Quadrature Counter or a Quadraturedecoder with an up/down counter). The up/down counter 34 is incrementedor decremented independently of any software using the A and Bhigh-resolution quadrature signals 38 associated with the highresolution track 14. The output from the up/down counter 34 can be ofany typical architecture or format for parallel or serial output, suchas SPI. The output from the up/down counter 34 provides absolute resultsindicative of the fine absolute position, without any furthersoftware-based processing, to maintain and continuously update the fineabsolute position of the device. This results in a fine or highresolution absolute position output signal that is achieved more quicklyand efficiently than conventional software-generated signals, as it isdelayed only by the logic timing associated with the up/down counter 34for each change in position, and not by any processing times associatedwith software or a processor.

As an alternative to using the A and B high-resolution quadraturesignals 38 to increment/decrement the counter 34, the input to thecounter 34 could be pulse and direction signals from the high resolutiontrack 14, as shown in FIG. 5.

In one application, a signal generated by the up/down counter 34 isfurther processed (e.g., by an additional logic circuit) to generate alow resolution signal or signals, such as three low resolution squarewave signals with a 120 degree difference, which can be used for motorcommutation detection and control. These commutation signals for motorcontrol, based on the absolute position value from the up/down counter34, are as accurate as a high resolution signal, more accurate than theconventional method that uses hall sensors to directly detectcoarse/reference track transition edges, and provides a faster responseas compared to software-generated commutation signals.

FIG. 6 illustrates a process for verifying the data output from theup/down counter 34. More specifically, it illustrates an operation thatcan be repeated at a lower frequency to constantly monitor whether thecounter output agrees with the fine absolute position or anglecalculation. Sometimes static discharges, such as nearby lightningstrikes, can negatively impact the up/down counter 34. To verify theaccuracy of the counter's output, periodic checking can occur. As shownin FIG. 6, the fine absolute position can be re-calculated at block 42in the same manner as described above for the initial, fine absoluteposition 30 calculation. This re-calculated value can be compared withthe actual output from the counter 34 at block 46. If there is aconfirmed mismatch indicating the counter 34 has a wrong value, thecounter 34 will be reloaded with the new counter initial value. An alarmcan also be used to notify of the mismatch/error. This process can beutilized with any of the absolute position sensing systems describedherein.

FIG. 7 illustrates a second absolute position sensing system 50. Thesecond sensing system 50 includes a first multi-polar magnetic ring orhigh resolution track 54, which includes sixty-four magnetic pole pairsor North/South pole pairs. Each pole of each North/South pole pair isthe same size (e.g., arc length). A second multi-polar magnetic ring ora reference track 58 is positioned concentrically within the highresolution track 54. In the embodiment shown, the reference track 58includes three magnetic pole pairs or North/South pole pairs arranged todefine a single-track Gray code.

A sensor and processing unit 62 is associated with the high resolutiontrack 54 and is configured to determine a position of the device overone of the North/South pole pairs of the high resolution track 54. Thesensor and processing unit 62 takes the form of a sensing ASIC, such asa Timken MPS160 or MPS512 chip, and is capable of determining theabsolute position of a target magnet within one North/South pole pair ofthe high resolution track 54 only. An array of Hall effect sensors 66 isassociated with the reference track 58 and is configured to determine acoarse absolute position of the device over the single-track Gray codesegment and to output a reference signal to the processing unit 62indicative of the coarse absolute position of the device over thesingle-track Gray code segment of the reference track 58. The distancebetween adjacent sensors 66 can be equal, but can be longer than a polelength of one or more poles on the reference track 58. The single-trackGray code of the reference track 58, when combined with the array offive Hall effect sensors 66, can provide thirty coarse positions.However, thirty positions are not enough to provide the fine absoluteposition because the high resolution track includes sixty-four polepairs.

In order to increase the resolution for the sixty-four pole pairs of thehigh resolution track 54, a third track or second reference track 70 isprovided. As illustrated in FIG. 7, the third track 70 is locatedconcentrically between the high resolution track 54 and the referencetrack 58, and includes sixteen North/South pole pairs, with each pole ofeach North/South pole pair being the same size (e.g., arc length). Thearc length of each pole pair of the third track 70 encompasses four polepairs of the high resolution track 54. In this manner, the thirty coursepositions identifiable by the reference track 58, in combination withthe output from the third track sensors 74, can identify the fineabsolute position over 4×16=64 pole pairs of the high resolution track54. If using a nine bit high-resolution interpolator, the encoder outputwill be 0, 1, . . . , 64×2{circumflex over ( )}9−1. An array of Halleffect sensors 74 (three sensors are shown) is associated with the thirdtrack 70 and communicates with the processing unit 62. This system 50can avoid using very small (narrow/short arc length) North/South polepairs, so as to allow using low cost sensors (such as Hall switchsensors) for the reference track 58 and the third track 70, while stillachieving increased resolution as compared to the first sensing system10. It should be noted that the respective positions of the tracks(i.e., inside or outside of one another) can be varied from theillustrated embodiment.

FIG. 8 illustrates a third absolute position sensing system 90 thatprovides even higher resolution than the second system 50. The thirdsensing system 90 includes a first multi-polar magnetic ring or highresolution track 94, which includes one hundred twenty-eight magneticpole pairs or North/South pole pairs. Each pole of each North/South polepair is the same size (e.g., arc length). A second multi-polar magneticring or a reference track 98 is positioned concentrically within thehigh resolution track 94. In the embodiment shown, the reference track98 includes four magnetic pole pairs or North/South pole pairs arrangedto define a single-track Gray code.

A sensor and processing unit 102 is associated, with the high resolutiontrack 94 and is configured to determine a position of the device overone of the North/South pole pairs of the high resolution track 94. Theprocessing unit 102 takes the form of a sensing ASIC, such as a TimkenMPS160 or MPS512 chip, and is capable of determining the absoluteposition of a target magnet within one North/South pole pair of the highresolution track 94 only. An array of Hall effect sensors 106 isassociated with the reference track 98 and is configured to determine acoarse absolute position of the device over the single-track Gray codesegment and to output a reference signal to the processing unit 102indicative of the coarse absolute position of the device over thesingle-track Gray code segment of the reference track 98. The distancebetween adjacent sensors 106 can be equal, but can be longer than a polelength of one or more poles on the reference track 98. The single-trackGray code of the reference track 98, when combined with the array of sixHall effect sensors 106, can provide forty-eight coarse positions.However, forty-eight positions are not enough to provide the fineabsolute position because the high resolution track includes one hundredtwenty-eight pole pairs.

In order to increase the resolution for the one hundred twenty-eightpole pairs of the high resolution track 94, a third track or secondreference track 110 is provided. As illustrated in FIG. 8, the thirdtrack 110 is located concentrically between the high resolution track 94and the reference track 98, and includes thirty-two North/South polepairs, with each pole of each North/South pole pair being the same size(e.g., arc length). The arc length of each pole pair of the third track110 encompasses four pole pairs of the high resolution track 94. In thismanner, the forty-eight course positions identifiable by the referencetrack 98, in combination with the output from the third track 110, canidentify the fine absolute position over 4×32=128 pole pairs of the highresolution track 94. For this higher resolution system 90, anothersensing ASIC 114, such as a Timken MPS160 or MPS512 chip, is associatedwith the third track 110 and is used in place of an array of Hall effectsensors. The increased resolution/sensitivity of the chip 114 enablesthe use of more pole pairs on the third track 110 to increase theoverall resolution of the encoder. Both the chip 114 and the array ofHall effect sensors 106 communicate with the processing unit 102. Inother embodiments, the chip 114 associated with the third track 110 andthe processing unit 102 associated with the high resolution track 94 canbe integrated into a single integrated circuit chip. It should be notedthat the respective positions of the tracks (i.e., inside or outside ofone another) can be varied from the illustrated embodiment.

FIG. 9 illustrates a fourth absolute position sensing system 130 thatprovides a resolution like the second system 50 in a different manner.The fourth sensing system 130 includes a first multi-polar magnetic ringor high resolution track 134, which includes sixty-four magnetic polepairs or North/South pole pairs. Each pole of each North/South pole pairis the same size (e.g., arc length). A second multi-polar magnetic ringor a reference track 138 is positioned concentrically within the highresolution track 134. In the embodiment shown, the reference track 138includes magnetic pole pairs or North/South pole pairs arranged todefine a plurality of single-track Gray code segments or sections. Asshown in FIG. 9, there are four single-track Gray code segments 140 a,140 b, 140 c, and 140 d on the reference track 138. Each Gray codesegment 140 a, 140 b, 140 c, and 140 d spans a ninety degree segment ofthe reference track 138. In other embodiments, there could be two,three, five, or more Gray code segments making up the reference track138.

A sensor and processing unit 142 is associated with the high resolutiontrack 134 and is configured to determine a position of the device overone of the North/South pole pairs of the high resolution track 134. Theprocessing unit 142 takes the form of a sensing ASIC, such as a TimkenMPS160 or MPS512 chip, and is capable of determining the absoluteposition of a target magnet within one North/South pole pair of the highresolution track 134 only. An array of Hall effect sensors 146 isassociated with the reference track 138 and is configured to determine acoarse absolute position of the device over any one of the single-trackGray code segments 140 a, 140 b, 140 c, and 140 d, and to output areference signal to the processing unit 142 indicative of the coarseabsolute position of the device over the respective single-track Graycode segment 140 a, 140 b, 140 c, and 140 d of the reference track 138.Each of the single-track Gray code segments 140 a, 140 b, 140 c, and 140d of the reference track 138, when combined with the array of five Halleffect sensors 146, can provide thirty coarse positions over each ninetydegree arc length. The distance between adjacent sensors 146 can beequal, but can be longer than a pole length of one or more poles on arespective single-track Gray code segment 140 a, 140 b, 140 c, and 140 dof the reference track 138.

In order to link the coarse positions of the four Gray code segments 140a, 140 b, 140 c, and 140 d to the high resolution track 134, a thirdtrack or second reference track 150 is provided. As illustrated in FIG.9, the third track 150 is located concentrically inside both of the highresolution track 134 and the reference track 138, and includes a singleNorth/South pole pair, with each pole of the single North/South polepair being the same or slightly different size (e.g., arc length). Anarray of Hall effect sensors 154 (three sensors are shown) is associatedwith the third track 150 and communicates with the processing unit 142.The output from the third track 150 can be used to determine theposition within one of the four Gray code segments 140 a, 140 b, 140 c,and 140 d. In this manner, the thirty course positions identifiable bythe each Gray code segment 140 a, 140 b, 140 c, and 140 d of thereference track 138, in combination with the output from the third track150, can identify the fine absolute position within the sixty-four polepairs of the high resolution track 134. It should be noted that therespective positions of the tracks (i.e., inside or outside of oneanother) can be varied from the illustrated embodiment.

The fourth system 130 of FIG. 9 can provide the same resolution as thesecond system 50 however the fourth system 130 provides some advantagesin terms of space and cost reduction. Specifically, as indicated by thearc length indicator 158, all of the Hall effect sensors 146 and 154, inaddition to the chip of the processing unit 142 are confined within lessthan a one hundred and eighty degree span, and as illustrated, about aone hundred twenty-five degree span of the encoder. This means that ifall of the sensors 146, 154 and the chip 142 are combined onto a singlechip, the chip size can be significantly reduced in comparison to asingle chip supporting all of the sensors of the second system 50. Thisopens up space over at least half of the encoder for additional hardwarecomponents. In fact, while not shown, in yet another embodiment, it isactually possible to achieve a further size reduction because thesensors 154 could even be moved closer together and centered on the topdead center position such that the arc length of the five sensors 146would be the limiting factor on the size of the chip. In thatembodiment, the circuit board could be confined to within about aseventy-five degree span of the encoder.

One of skill in the art will understand that with any of the disclosedembodiments having three circular tracks, the relative positions of thetracks can be selected as desired such that any of the tracks can be theoutside, inside, or middle track.

Just as described with the first system 10, each of the systems 50, 90,and 130 can utilize the up/down data counter 34 and signal processingflow outlined in FIG. 4. In yet other embodiments of signal processingfor each of the systems 10, 50, 90, and 130, an alternative signalprocessing flow shown in FIG. 10 can be utilized. As shown in FIG. 10,hardware or software can be utilized to provide an adding function atblock 170. This can be used in applications when an offset is desiredfor the encoder. In this flow, the initial value 30 and the output fromthe up/down counter 34 are separately input into the adder 170, whichcan apply the desired offset function and then output the resultingabsolute position signal.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A system for determining an absolute position ofa device, the system comprising: a high resolution track having aplurality of North/South pole pairs, each pole of each North/South polepair being a same size; a sensor and processing unit associated with thehigh resolution track and configured to determine a position of thedevice over one of the North/South pole pairs of the high resolutiontrack; a reference track having a plurality of North/South pole pairsarranged to define a single-track Gray code segment; an array of Halleffect sensors associated with the reference track and configured todetermine a coarse absolute position of the device over the single-trackGray code segment and to output a reference signal to the sensor andprocessing unit indicative of the coarse absolute position of the deviceover the single-track Gray code segment, wherein the sensor andprocessing unit combines the reference signal with the position of thedevice over one of the North/South pole pairs of the high resolutiontrack to determine an initial, fine absolute position of the device; andan up/down hardware counter operable to increment the initial fineabsolute position determined by the sensor and processing unit using asignal generated from the high resolution track, and without any furthersoftware-based processing, to maintain and continuously update the fineabsolute position of the device.
 2. The system of claim 1, wherein thesingle-track Gray code segment extends over the entire reference track.3. The system of claim 2, further comprising a third track and at leastone sensor associated with the third track.
 4. The system of claim 3,wherein the at least one sensor associated with the third track is anarray of Hall effect sensors.
 5. The system of claim 3, wherein the atleast one sensor associated with the third track is an array of Halleffect sensors mounted on an ASIC chip.
 6. The system of claim 3,wherein the third track has more North/South pole pairs than thereference track and fewer North/South pole pairs than the highresolution track.
 7. The system of claim 3, wherein the third track ispositioned concentrically between the high resolution track and thereference track.
 8. The system of claim 3, wherein the third track has8-64 North/South pole pairs and the high resolution track has 16-256North/South pole pairs.
 9. The system of claim 1, wherein thesingle-track Gray code segment is one of a plurality of single-trackGray code segments on the reference track, and wherein the systemfurther includes a third track and at least one sensor associated withthe third track to determine a location within one of the plurality ofsingle-track Gray code segments.
 10. The system of claim 9, wherein thethird track is positioned concentrically inside both of the highresolution track and the reference track, concentrically outside both ofthe high resolution track and the reference track, or concentricallybetween the high resolution track and the reference track.
 11. Thesystem of claim 9, wherein the third track has only a single North/Southpole pair.
 12. The system of claim 9, wherein the high resolution track,the reference track, and the third track are circular tracks arrangedconcentrically, and wherein the array of Hall effect sensors associatedwith the reference track, the at least one sensor associated with thethird track, and the sensor and processing unit are all confined withinless than a one hundred and eighty degree span of the circular tracks.13. The system of claim 1, wherein the array of Hall effect sensorsincludes 5-8 Hall effect sensors.
 14. The system of claim 1, wherein thehigh resolution track and the reference track are circular tracksarranged concentrically.
 15. The system of claim 1, wherein the highresolution track and the reference track are linear tracks arranged inparallel.
 16. The system of claim 1, further comprising an adderoperable to receive the initial, fine absolute position of the deviceand a signal from the up/down counter and to apply an offset to theabsolute position of the device.
 17. The system of claim 1, wherein thesignal generated from the high resolution track and used to update thefine absolute position of the device is one of a high resolutionquadrature signal, a pulse signal, or a direction signal provided to theup/down counter.
 18. The system of claim 1, wherein a signal generatedby the up/down counter is further processed to generate a low resolutionsignal including three low resolution square wave signals with a 120degree difference for use in motor commutation detection and control.